Gelled floating roof for storage tanks and pits and process for forming same

ABSTRACT

A novel and inexpensive floating roof for tank and pit storage of crude oil and other petroleum products is formed in place by gelling a thin surface layer of oil using gelling agents in low concentration. The gelling agent employed is the reaction product of a diisocyanate and either an amine or an alcohol, which reaction product is a urea-type molecule which ultimately forms the gel with the oil. The layer of gelled oil floats on the surface of the material being stored and follows changes in its level. In sloping-wall pits the gelled layer readily adjusts to the changing wall contours while at the same time substantially reducing volatile and wind entrainment losses, fire hazards and water entrapment.

United States Patent Corino et al.

[4 1 Feb.l, 1972 [72] inventors: Edward R. Corino, Belleville; Gerard P.

Canevari, Cranford, both of NJ.

[73] Assignee: Esso Research and Engineering Company [22] Filed: July 30, 1968 211 Appl. No.: 748,587

[56] References Cited UNITED STATES PATENTS 6/1957 Veatch et al ..21/60.5

2,797,l4l 6/1957 Veatch ..21l60.5 3,355,269 1 1/1967 Winkler ..252/3l6 X 3,455,848 7/1969 Yoncoskie et al. ..252/316 X Primary Examiner-Richard D. Lovering Attorney-Manahan and Wright and Donald F. Wohlers [57] ABSTRACT A novel and inexpensive floating roof for tank and pit storage of crude oil and other petroleum products is formed in place by gelling a thin surface layer of oil using gelling agents in low concentration. The gelling agent employed is the reaction product of a diisocyanate and either an amine or an alcohol, which reaction product is a urea-type molecule which ultimately forms the gel with the oil. The layer of gelled oil floats on the surface of the material being stored and follows changes in its level. In sloping-wall pits the gelled layer readily adjusts to the changing wall contours while at the same time substantially reducing volatile and wind entrainment losses, fire hazards and water entrapment.

13 Claims, No Drawings GELLED FLOATING ROOF FOR STORAGE TANKS AND I'I'IS AND PROCESS FOR IORMING SAME BACKGROUNDOFTI'IE INVENTION Very large tanks and/or pits for the storage of crude oil or similar petroleum products are now being employed throughout the world due to their ability to produce low per barrel storage costs. One of the major problems involved in the use of these large tanks or storage pits relates to the type of covering to be provided over the open mouth. In this regard it will be appreciated that unless suitable cover means are'provided, large losses through evaporation willbe suffered. In addition to evaporation'losses, problems in the form of fire hazards, air pollution, and entrapment of dispersed water are also encountered.

In addition to the above problems, additional problems may be caused by the vapor phase of the stored liquid, since this phase often contains a layer or region of explosive composition which can be ignited by static electricity. Also, when a liquid mixture is stored having constituents of different volatilities, such as jet fuel, for example, the more highly volatile liquids are lost at a higher rate than the rest of the composition and, hence, the stored liquid is degraded in composition. Wind entrainment of oil from the surface can cause pollution and tire hazards downwind of the storage pit. Furthermore, unless suitable coverage is provided, certain stored liquids being exposed to direct sunlight may be subjected to photochemical decomposition.

Prior to the present invention, many attempts have been made to design apparatus which would solve or attempt to solve the above-enumerated problems. These have often invalved-complex, rigid floating covers having expensive seals between their peripheries and the walls of the tank. Such rigid covers cannot easily be installed in existing tanks and have various limitations imposed upon their ultimate sire. Furthermore, their use for open pit storage has been severely limited in that itis difficultto employ rigid floating roofs which will conform to the sloping sides of conventionalstorage pits. The prior art also contains several examples of nonrigid floating covers, but these either required complex associated apparatus or a combination of floats and of flexible sheets, which due to the bulk of the floats is difficult to install and maintain. None of the above solutions have the additional advantage of contact with substantially the entire surface of the liquid being stored, which contact inhibits the initial transfer of molecules from the liquid to the vapor phase.

The present invention contemplates the gelling of a thin layer of oil at the surface of the reservoir to create an effective and inexpensive floating roof for large tanks and pits. Since only a thin layer of oil is gelled (e.g'., l to 4 inches) using gelling agents at concentrations, for example, of about 3 weight percent based on the oil in the gel, the roof is extremely inexpensive to form and maintain. The roof obtained by the process of the instantinvention retains the economic incentives associated with large tank or pit storage while reducing the cost. It also eliminates the objectionable characteristics of open tank or open pit storage. Because of the seasonal demand for many petroleum products such as fuel oil, producers are often forced to store in such open pits. For example, at Lake Maracaibo there is an openstorage pit I feet deep with a surface area of 12% acres. It will be appreciated that evaporation losses from this pit are enormous. Such pits and other open storage vessels may be efficiently and effectively covered according to the teachings of the instant invention, whereby the large evaporation losses heretofore encountered are eliminated.

SUMMARY OF THE mveunou According to the process of theinstant invention an inexpensive and effective floating roof for large tanks and open pits is obtained by gelling a thin layer of oil at the surface of the reservoir. The gelled layer, which is preferably between in concentrations ranging from about 2.0 to about 4.0 percent and preferably about 3 percent. Since the only other component is the oil itself, the-roof is inexpensive to form and maintain, thus the economic incentives associated with large tank or pit. storage are retained while the objectionable characteristics of such storage are eliminated. To meet the economic criteria, the gelling agents must be effective in small amounts and react quickly in situ with a minimum of mixing. These requirements are met by a two-part gelling agent composed of adiisocyanate and an amine. The addition of agents to the oil at approximately 3 percent concentration produces a gel almost instantaneously. A preferred gelling system for the process of the instant invention is obtained when l percent toluene diisocyanate (mixed isomers 2,4 and 2,6) and 2 percent cocoamine are added to the surface layer of the oil being stored. Alternatively, a slower reacting system using about 0.7 percent toluene diisocyanate and 2.3 percent beta amine may be employed.

DETAILED DESCRIPTION OF THE INVENTION As hereinabove indicated, an effective and inexpensive floating roof for large storage tanks or pits may be achieved by the addition of small amounts of gel-forming compounds. It will be appreciated that no mixing other than that associated with the addition of the gel formers is needed, since the particulargelling agents employed are soluble in the material to be gelled. 'The gelling agents are the precursors of an ureatype molecule which ultimately forms the gel with the oil. This compound is formed in situ by reaction between the precursor gelling agents. This gel structure provides sufficient strength and flexibility for the instant application. Since the gel precursors are added as low-viscosity liquids (or as oil-soluble solids), applicaticnof the process of the instant invention is readily accomplished. For example, the process of the instant invention may be practiced by sprayingthe gel-forming agents onto the oil surface thereby forming the desired gel. Another method of utilizingthe process of the instant invention is by forming the gel by mixing gelling agents in the material to be gelledina nozzle or pumpand then simultaneously dischargingthe material through the nozzle onto the uppemrost surface of the material being stored. This latter method finds ready application when using solid gelling materials or when it is desired to form a'protective roof by gelling a material other than the particularmaterial being stored or when it is desired to mix other materials with the gel.

As hereinabove indicated, gelling agents which are suitable for use in the process of the invention fall basically into classes of compounds generally designated isocyanates, amines, and alcohols. Each of these classeshas numerous compounds, as will bereadily appreciated by those skilled in the chemical arts. The selection of particular agents from these classes is dictated by the needs of a given situation, i.e., the material to be gelled and-gel strength requirements and reaction rate. Gel properties can be varied with composition and concentration of the agents being used as well.

The following compounds have been found to be particuc, 1% c,, was

c,, are c,, as

c,, sans c,, ms Unsaturated c,, 5.0a

The compound p-phenetidine is an aromatic. amine with the 0.5 and 4 inches thick, is obtained by the use of gelling agents structural formula:

Suitable beta amines are aliphatic primary amines of carbon number C, --C in which the amine group is attached to the beta carbon atom, i.e.,

a( 2)u(3IICH Suitable alcohols for use in the process of the instant invention include dodecyl alcohol and decyl alcohol. An example of the reaction producing the gel-forming molecule is:

Oocoamine Tolune diisocyanate Urea-type gel-forming molecule where R is an aliphatic or aromatic organic radical; or by the solution in one of the precursors of an inert blowing agent such as Freon which is released during the course of reaction. Still another method for increasing the buoyancy (or decreasing the density) of the gel is to use an oil for the gelled roof which has a lower density than the oil being stored.

From the above description it is seen that the process of the instant invention provides a method whereby an effective and economical floating roof for large tank and pit storage of crude oil or other distillates may be achieved. The instant roof, while being inexpensive, is also easy to form and maintain. Thus, small breaks in the gel can be self-healing." Large breaks can be readily repaired by application of a small amount of the gelling agent. The gel is self-buoyant and supported by flotation on the oil surface itself. No structural members or buoyancy aids are needed. If desired, additional buoyancy may be readily obtained according to the methods outlined above, e.g., by the encapsulation of microballoons in the gel or by foaming in place. The gel is rigid and continuous, thus giving even distribution over the surface despite wind action. This is markedly different from liquid surface coverings or coverings made by flotation of discrete buoyant solids. The gel will also deform and flow if its stress limit is exceeded and will reform when the stress is removed. Thus, the gelled roof can follow contours of sidewalls. As indicated above, this is of particular importance when storing in large sloping-sided open pits.

The gelled roof of the instant invention also has very low vapor pressures, which means that the fire hazard normally associated with stored hydrocarbons is greatly reduced since the gel is difficult to ignite. burns slowly and, unlike a liquid, does not readily flow. Furthermore, the gel is impermeable to water which eliminates entrapment of water in the oil in a dispersed form.

While the instant invention has been described in considerable detail, this is done by way of illustration and not by way of limitation. Hence, in determining the full scope of the invention, reference should be had to the following appended claims.

What is claimed is:

l. A process for forming a floating roof on the surface of a petroleum product reservoir which comprises essentially the steps of adding a gelling agent to the surface layer of the petroleum product, wherein said gelling agent is selected from the group consisting of a reaction product formed by reacting a member of the group consisting of 2,4 and 2,6 isomers of toluene diisocyanate, hexamethylene diisocyanate, a-naphthyl diisocyanate, and p,p'-diphenyl methane diisocyanate with a member of the group consisting of dodecyl amine, 9-Octadecanoic amine, cocoamine, p-phenetidine, aliphatic primary amines of carbon number C, C in which the amine group is attached to the beta carbon atom, dodecyl alcohol, decyl alcohol and mixtures thereof, the concentration of said gelling agent therein being in the range of from about 2.0 to about 4.0 weight percent based on said petroleum product.

2. The process of claim 1 wherein said gelling agent is formed by reacting the 2,4 and 2,6 isomers of toluene diisocyanate and cocoamine.

3. The process of claim 1 wherein said gelling agent is formed by reacting toluene diisocyanate with a beta amine selected from the group consisting of aliphatic primary amines of carbon number C C in which the amine group is attached to the beta carbon atom.

4. The process of claim 1 wherein said roof is formed in a thickness of from about 0.5 inches to about 4 inches.

5. A process for producing a gelled petroleum product floating roof having a thickness of from about 0.5 to about 4.0 inches on a petroleum product reservoir which comprises adding to said petroleum product from about 0.6 to about 1.4 weight percent of toluene diisocyanate based on the amount of petroleum product to be incorporated in said gelled roof and then adding from about 0.6 to about 2.7 weight percent based on said amount of petroleum product of cocoamine whereby the reaction product of said toluene diisocyanate and said cocoamine gels said petroleum product to produce said gelled floating roof on the surface of said petroleum product in said reservoir.

6. The process of claim 5 wherein said toluene diisocyanate is selected from the group consisting of the 2,4 and 2,6 isomers of toluene diisocyanate and mixtures thereof.

7. The process of claim 5 wherein the petroleum product and the toluene diisocyanate and cocoamine are mixed and dispersed onto the surface of the product in said reservoir through a nozzle.

8. The process of claim 5 wherein the buoyancy of said floating roof is increased by incorporating therein microballoons of a material selected from the group consisting of glass, plastic and expanded shale.

9. The process of claim 5 wherein the buoyancy of said floating roof is increased by partially foaming the gelled roof during its formation.

10. The process of claim 9 wherein the gel is foamed by gas generation, said generation being obtained by reacting water and a diisocyanate.

11. The process of claim 9 wherein the gel is foamed by incorporating an inert blowing agent in the toluene diisocyanate, which agent is released during the course of the reaction between said toluene diisocyanate and said cocoamine.

12. A floating roof for'a petroleum product storage container, which consists essentially of a buoyant gel formed by the combination of a gelling agent with the surface layer of the the amine group is attached to the beta carbon atom, dodecyl alcohol, decyl alcohol and mixtures thereof.

13. The floating roof of claim 12 wherein said roof is formed in a thickness of from about 0.5 inch to about 4 inches and the concentration of said gelling agent therein is in the range of from about 2.0 to about 4.0 weight percent based on said petroleum product.

l 0' i III II 

2. The process of claim 1 wherein said gelling agent is formed by reacting the 2,4 and 2,6 isomers of toluene diisocyanate and cocoamine.
 3. The process of claim 1 wherein said gelling agent is formed by reacting toluene diisocyanate with a beta amine selected from the group consisting of aliphatic primary amines of carbon number C12-C20 in which the amine group is attached to the beta carbon atom.
 4. The process of claim 1 wherein said roof is formed in a thickness of from about 0.5 inches to about 4 inches.
 5. A process for producing a gelled petroleum product floating roof having a thickness of from about 0.5 to about 4.0 inches on a petroleum product reservoir which comprises adding to said petroleum product from about 0.6 to about 1.4 weight percent of toluene diisocyanate based on the amount of petroleum product to be incorporated in said gelled roof and then adding from about 0.6 to about 2.7 weight percent based on said amount of petroleum product of cocoamine whereby the reaction product of said toluene diisocyanate and said cocoamine gels said petroleum product to produce said gelled floating roof on the surface of said petroleum product in said reservoir.
 6. The process of claim 5 wherein said toluene diisocyanate is selected from the group consisting of the 2,4 and 2,6 isomers of toluene diisocyanate and mixtures thereof.
 7. The process of claim 5 wherein the petroleum product and the toluene diisocyanate and cocoamine are mixed and dispersed onto the surface of the product in said reservoir through a nozzle.
 8. The process of claim 5 wherein the buoyancy of said floating Roof is increased by incorporating therein microballoons of a material selected from the group consisting of glass, plastic and expanded shale.
 9. The process of claim 5 wherein the buoyancy of said floating roof is increased by partially foaming the gelled roof during its formation.
 10. The process of claim 9 wherein the gel is foamed by gas generation, said generation being obtained by reacting water and a diisocyanate.
 11. The process of claim 9 wherein the gel is foamed by incorporating an inert blowing agent in the toluene diisocyanate, which agent is released during the course of the reaction between said toluene diisocyanate and said cocoamine.
 12. A floating roof for a petroleum product storage container, which consists essentially of a buoyant gel formed by the combination of a gelling agent with the surface layer of the stored petroleum product wherein said gelling agent is selected from the group consisting of a reaction product formed by reacting a member of the group consisting of 2,4 and 2,6 isomers of toluene diisocyanate, hexamethylene diisocyanate, Alpha -naphthyl diisocyanate, and p,p''-diphenyl methane diisocyanate with a member of the group consisting of dodecyl amine, 9-octadecanoic amine, cocoamine, p-phenetidine, aliphatic primary amines of carbon number C12-C20 in which the amine group is attached to the beta carbon atom, dodecyl alcohol, decyl alcohol and mixtures thereof.
 13. The floating roof of claim 12 wherein said roof is formed in a thickness of from about 0.5 inch to about 4 inches and the concentration of said gelling agent therein is in the range of from about 2.0 to about 4.0 weight percent based on said petroleum product. 